Fix config/hackystack-*.php.example files to be empty and move GitLab examples to `.example-gitlab`

Summary

The community best practice is that .php.example files are the empty templates to use for your environment configuration, and should not be populated with real example data.

Some of the .example files in earlier commits include the GitLab implementation examples and need to be renamed.

Suggested Implementation

1. Rename config/hackystack-auth-groups.php.example to config/hackystack-auth-groups.php.example-gitlab
2. Rename config/hackystack-auth-provider-fields.php.example to config/hackystack-auth-provider-fields.php.example-gitlab
3. Rename config/hackystack-cloud-realms.php.example to config/hackystack-cloud-realms.php.example-gitlab
4. Create new files with empty return [] arrays since the instructions are already documented in the comment block at the top of the file.